Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Patent
1997-05-15
1999-01-12
Wong, Don
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
315 82, 315 94, H05B 3702
Patent
active
058595074
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to a circuit arrangement for starting and operating a high-pressure gas discharge lamp operating by controlled alternating current, in particular for use in motor vehicle headlamps, of the type wherein the voltage (U.sub.B) of a direct voltage source is converted to a higher value by means of a direct current/direct current converter, and a controlled alternating current (I.sub.L) for supplying the high-pressure gas discharge lamp is generated from this current (U.sub.B) by a controlled full-bridge circuit that can be operated either with direct or alternating current, and for which a control circuit for actuating the full bridge circuit, as well as an ignition device for igniting the high-pressure gas discharge lamp are provided.
A series reactor for starting and operating alternating current high-pressure gas discharge lamps is known from German patent application DE 41 36 486 A1, wherein the reactor is supplied from a direct voltage source, e.g. the battery of a motor vehicle. A stabilized and/or power-controlled direct voltage with a higher voltage value is initially generated from the direct voltage of the direct voltage source by means of a DC/DC converter. The alternating current necessary for the operation is then generated from this higher voltage with the aid of a controlled full bridge circuit. The full bridge circuit can be operated either with direct current or also with alternating current. The full bridge circuit is controlled by a control circuit, and an ignition device is provided for igniting the high-pressure gas discharge lamp.
With this known series reactor, the bridge circuit is operated with direct current during the start-up to achieve a rapid and reliable ignition as well as to reach rapidly and reliably a stable operating state without flickering of the lamp. A signal is generated via a status determination device, provided the high-pressure gas discharge lamp has been ignited successfully. This signal is transmitted via a delay circuit to the control circuit for the full bridge circuit and ensures that the full bridge circuit is switched only after the predetermined delay time from the direct current operation to the alternating current operation.
The problem with high-pressure gas discharge lamps operating by alternating current, in particular cold lamps, generally is that the high-pressure gas discharge lamp goes out during the pole reversal process and that it must be ignited again following the pole reversal. The voltage required for a re-ignition determines the necessary open-circuit voltage of the supply circuit, meaning in this case the voltage present at the output of the full bridge circuit.
SUMMARY AND ADVANTAGES OF THE INVENTION
The problems according the prior art arrangements as discussed above are essentially overcome according to the present invention in that in a circuit arrangement of the type initially described above, the control circuit controls the full bridge circuit such that the duration of the half-wave phases of the alternating current (I.sub.L) that supplies the high-pressure gas discharge lamp is variable and is varied in dependence on the respective temperature of the electrodes of the high-pressure gas discharge lamp.
In contrast to the prior known circuit arrangement, the inventive circuit arrangement for starting and operating a high-pressure gas discharge lamp operating by controlled alternating current, with the features mentioned above, has the advantage that it keeps the open-circuit voltage of the supply circuit low. As a result of this, the cost-effectiveness ratio of the total circuit arrangement becomes more favorable.
In accordance with the invention, this is achieved principally through an adaptive adjustment of the half-wave times of the alternating circuit or voltage supplied to the gas discharge lamp to the instantaneous temperature of the electrodes for the high-pressure gas discharge lamp. Typically, it is provided in this case that the control circuit controls the full bridge circuit in such a way
REFERENCES:
patent: 5055742 (1991-10-01), Jurrel
patent: 5233273 (1993-08-01), Waki et al.
patent: 5469027 (1995-11-01), Uchihashi et al.
Kunitz Norman N.
Robert & Bosch GmbH
Spencer George H.
Vu David H.
Wong Don
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